The present invention relates to a correction signal generating circuit for generating a correction signal for correcting a deflected position of an electron beam. The correction signal generating circuit according to the present invention can be advantageously used as a registration correcting circuit for a multi-tube type color television camera. Additionally, the correction signal generating circuit according to the invention can be employed not only for the correction of registration in the multi-tube type television camera but also as a dynamic focusing wave generator for a single tube type color camera, a convergence circuit in a color television receiver, a shading correction wave generator for a television signal and others.
Heretofore, a so-called three-tube type color television camera which includes three imaging tubes (also referred to as the image pick-up tubes) corresponding to three primary colors (red, green and blue), respectively, has been used in the field of the television broadcasting and for applications where high image quality is required.
In addition to the three tube type color television (TV) camera mentioned above, there are known a two-tube type color TV camera which includes one imaging tube destined for picking up a luminance signal and the other for an obtained chrominance signal and a four-tube type color television camera which includes a fourth image pick-up tube for detecting the luminance signal in addition to the three tubes for detecting the primary color signals of red, green and blue, respectively. As a technological feature common to these multi-tube color television cameras, so-called registration adjustment techniques are required for superposing the images produced by the individual imaging tubes. In general, in the case of the television camera in which the image pick-up tubes are employed, tolerances in manufacturing the electron gun and the deflection coil assembly as well as electrooptical distortions attributable to these tolerances and peculiar to the type of deflection system as adopted give rise to the problem of various geometric distortions being produced.
In the hitherto known multi-tube type color television camera as well as the camera which is designed especially for the measuring purpose in which the problem of the geometric distortion is serious, the deflection current is superposed with a correction wave such as, for example, a parabolic wave and saw-tooth wave or alternatively the deflection current is modulated with the correction wave for correcting the geometric distortion mentioned above.
The hitherto known method of correcting the geometric distortion by modifying the deflection of the electron beam in the manner described above is effective for correcting the distortion so far as the distortion of low order is concerned. However, in the present state of the technology of the color television camera such as the multi-tube type color TV camera, there arises a demand for adjustment of registration at a higher precision, which demand can no longer be satisfied by the correction only of the distortion of low order. In particular, in the case of a high definition television camera in which the number of the scanning lines exceeds 525 lines of the existing system, a higher precision is required for the image registration.
To meet the above demand, there has recently been developed a digital resistration circuit which is designed to correct the distortions of high order by resorting to the use of a computer and a memory system (reference is to be made to Japanese Patent Application Laid-Open No. 2166/1982).
According to the proposed digital registration system, values for correction are given for every intersection of division lines which divide the screen of television in both horizontal and vertical directions.
The values for correction given for every intersection have to be read out in a sequential order in synchronism with the scanning period. Further, once the values for correction have been determined, the values read out every frame or field must remain unchanged. Accordingly, a memory for storing the correction values for every intersection is required. Further, since the correction values are given to the intersections in one-to-one correspondence, correction values have to be obtained through interpolation for the scanning lines present between the adjacent correction values in the horizontal and vertical direction.
It has however been found that in a digital registration system in which the linear interpolation is effected in the vertical direction, such an undesirable phenomenon that outputs of the image pick-up tubes undergo rapid changes at the intersections where the correction for registration is carried out, i.e. phenomenon of the so-called "shading" does occur to a disadvantage. Since the quantity of correction for registration is naturally different among the image pick-up tubes for red, green and blue colors, the shading makes appearance as color nonuniformity and luminance non-uniformity to degrade remarkably the image or picture quality.